某地区花岗石三轴蠕变试验及其损伤分岔特性研究

 以某地区花岗岩为例，在分级加载条件下对岩石的蠕变特性进行三轴压缩蠕变试验研究，试验结果表明：岩石变形从稳态蠕变进入加速蠕变阶段存在一个应力阈值，当应力低于该阈值时，岩石内部的原始裂隙和孔隙在低应力水平下挤压密实，产生微细观的线黏弹性变形，蠕变变形以平缓的速率增长并最终趋于稳定，此时岩石的流变参数保持恒定；当应力超过该阈值时，在较高应力水平的持续作用下，岩石内部有大量细观分布裂纹产生并且迅速发展，损伤急剧演化累积，导致岩石流变参数发生突变。采用FLAC3D对花岗岩三轴蠕变试验进行三维数值模拟，得到岩石蠕变进入加速阶段的应力阈值。最后结合固体力学的分岔理论，从流变参数的角度考虑，对广义开尔文模型引入损伤变量，建立能够反映岩石加速蠕变阶段的损伤演化方程，对岩石进入加速蠕变阶段后由于参数突变引发的分岔力学特性进行分析，确定引起岩石发生分岔行为的流变参数以及岩石蠕变变形的分岔点。计算结果表明，基于考虑损伤影响的有效初始弹性模量得到的计算曲线与试验曲线的吻合情况较为理想。

STUDY ON DAMAGE AND BIFURCATION PROPERTIES OF SOME GRANITES BASED ON TRIAXIAL CREEP EXPERIMENT

The creep properties of granite specimen are studied under triaxial compression creep experiment with the method of step loading，and the experimental results show that there exists a stress threshold in the creep deformation of rock from stable creep phase to accelerating creep phase. If the applied load is lower than the threshold，the initial microcracks and pores in rock are compacted under the lower stress level and the microcosmic linear visco-elastic deformation will come into being in the microstructure of rock，so the creep rate of rock is uniform and the deformation will tend towards a steady value，and the rheological parameters are invariable under the lower stress level；when the applied load is bigger enough to exceed the threshold，a mass of microcracks come into being，grow quickly，and the damage evolvement is rapid，this will induce the change of rheological parameters of rock. To obtain the value of this stress threshold，the triaxial compression creep experiment of rock is simulated with the method of three-dimensional numerical simulation and the stress threshold is obtained. The damage variables are introduced into the generalized Kelvin model，and the corresponding damage evolution equations which are able to reflect the characteristics of the accelerating creep phase of rock are set up. Furthermore，by applying the bifurcation theory of solid mechanics，the bifurcation behavior of rock due to the change of rheological parameters after the deformation turning into the accelerating creep phase is studied，the rheological parameters，which cause the creep bifurcation behavior of rock，are determined and the bifurcation points are obtained. The results show that the calculated curve based on the effective initial elastic modulus considering damage factor agrees well with the experiment curve.